#define _CRT_SECURE_NO_WARNINGS 1
class Solution {
public:
    bool hasCycle(ListNode* head) {
        struct ListNode* fast = head, * slow = head;
        while (fast && fast->next)
        {
            slow = slow->next;
            fast = fast->next->next;

            if (slow == fast)
            {
                return true;
            }
        }
        return false;
    }
};